Libxml upgrade

Creating a generic interface between Tritium and Gokogiri (https://moovweb.atlassian.net/browse/PFST-49)
We don't have a coding convention, but GO does suggest one, and that generally is to drop the 'Get' in getters.
http://golang.org/doc/effective_go.html#Getters
not required as we don't have a coding convention, but just an FYI.